<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>js</title>
</head>
<body>
	<h1>aaaaaaaaaaaaaaaaaaaaa</h1>
	<h1>aaaaaaaaaaaaaaaaaaaaa</h1>
	<h1>aaaaaaaaaaaaaaaaaaaaa</h1>
	<h1>aaaaaaaaaaaaaaaaaaaaa</h1>
</body>

<script>
	document.documentElement.style.background='#00f';//documentElement指的是html,最外层
	document.body.style.background='#f0f';
</script>
</html>